1. Field of the Invention
This invention generally relates to a coating of fast dissolution or absorption on an implantable device.
2. Description of the Background
Blood vessel occlusions are commonly treated by mechanically enhancing blood flow in the affected vessels, such as by employing a stent. Stents are used not only for mechanical intervention but also as vehicles for providing biological therapy. To affect a controlled delivery of an active agent in stent based therapy, the stent can be coated with a biocompatible polymeric coating. The biocompatible polymeric coating can function either as a permeable layer or a carrier to allow a controlled delivery of the agent. A continuing challenge in the art of implantable stents is to provide a coating that possesses good biobeneficial properties, which refer to good biocompatibilities in both the acute and chronic timeframes.
Generally, a polymer forming a coating composition for an implantable device has to be at least biologically benign. Additionally, the polymer could have a therapeutic effect either additively or synergistically with the bioactive agent. The polymer is preferably biocompatible. To provide for a coating that is biologically benign, various compositions have been used with limited success. For example, coating compositions containing poly(ethylene glycol) have been described (see, for example, U.S. Pat. No. 6,099,562). One of the needs in the art is to provide for a stent that has favorable long-term biological properties. However, under certain circumstances, it is documented that polymer and remaining drugs on the stents are major factors in causing late clinical effects such as late stent thrombosis, in stent artherosclerosis, and late stent malapposition.
The various embodiments described below address the above described problems.